Colored conversion layers on metallic substrates

ABSTRACT

A chromium-free treatment solution for producing colored or fluorescing corrosion prevention layers on metal surfaces which contains phosphoric acid and/or at least one fluoro acid of one or more elements from the group consisting of B, Si, Ti, Zr and Hf or anions thereof and at least one organic polymer, the organic polymer being capable of binding to the metal surface through oxygen and/or nitrogen atoms, and having covalently bonded groups which appear colored to the human eye or which fluoresce discernibly to the human eye on exposure to UV light.

CROSS-REFERENCE

This application is a continuation under 35 USC Sections 365 (c) and 120of International Application No. PCT/EP2005/000769, filed Jan. 27, 2005and published Dec. 8, 2005 as WO 2005/116294 which claims priority to DE10 2004 022 565.6 filed May 7, 2004, each of which is incorporatedherein by reference in its entirety.

FIELD OF THE INVENTION

This invention relates generally to the chemical surface treatment ofzinc or galvanized steel, aluminium, magnesium or alloys thereof and,more particularly, to chromium-free conversion processes for such metalsurfaces, i.e. chemical treatment processes which lead to the formationof a surface layer in which both cations of the treated metal surfaceand ions from the treatment solution are incorporated. The chromium-freecoating is colored so that it is possible to tell by simple visualinspection whether an adequate conversion layer has been formed. Thefunction of this conversion layer is to reduce the tendency of the metalsurface towards corrosion and to establish good adhesion between themetal surface and an organic coating applied to the conversion layer,for example in the form of a paint or an adhesive.

DISCUSSION OF THE RELATED ART

Extensive prior art exists on the production of chromium-free conversionlayers on the metal surfaces mentioned.

U.S. Pat. No. 5,129,967 discloses treatment baths for the no-rinsetreatment (or “dried in place conversion coating”) of aluminium whichcontain

a) 10 to 16 g/l polyacrylic acid or homopolymers thereof,

b) 12 to 19 g/l hexafluorozirconic acid,

c) 0.17 to 0.3 g/l hydrofluoric acid and

d) up to 0.6 g/l hexafluorotitanic acid.

EP-B-8 942 discloses treatment solutions, preferably for aluminium cans,containing

a) 0.5 to 10 g/l polyacrylic acid or an ester thereof and

b) 0.2 to 8 g/l of at least one of the compounds H₂ZrF₆. H₂TiF₆ andH₂SiF₆, the pH value of the solution being below 3.5.

Other polymers which may be used in similar treatment baths aredisclosed in WO 02/20652.

U.S. Pat. No. 4,992,116 describes treatment baths for the conversiontreatment of aluminium with pH values of about 2.5 to 5 which contain atleast three components:

-   -   a) phosphate ions in concentrations of 1.1×10⁻⁵ to 5.3×10⁻³        mol/l, corresponding to 1 to 500 mg/l,    -   b) 1.1×10⁻⁵ to 1.3×10⁻³ mol/l of a fluoro acid of an element        from the group consisting of Zr, Ti, Hf and Si (corresponding to        1.6 to 380 mg/l, depending on the element) and    -   c) 0.26 to 20 g/l of a polyphenol compound obtainable by        reaction of poly(vinylphenol) with aldehydes and organic amines.

WO 92/07973 teaches a chromium-free treatment process for aluminiumwhich uses 0.01 to about 18% by weight of H₂ZrF₆ and 0.01 to about 10%by weight of a3-(N—C₁₋₄-alkyl-N-2-hydroxyethylaminomethyl)-4-hydroxystyrene polymer asessential components in an acidic aqueous solution. Optional componentsare 0.05 to 10% by weight of dispersed SiO₂, 0.06 to 0.6% by weight of asolubilizer for the polymer and surfactant. The polymer mentioned comesunder the group of “reaction products of poly(vinylphenol) withaldehydes and organic amines containing hydroxyl groups” described inthe following which suitable for use in accordance with the presentinvention.

WO 00/71626 discloses a chromium-free corrosion-inhibiting compositioncontaining water and

-   -   a.) 0.5 to 100 g/l hexafluoro anions of titanium(IV),        silicon(IV) and/or zirconium(IV)    -   b.) 0 to 100 g/l phosphoric acid    -   c.) 0 to 100 g/l of one or more compounds of cobalt, nickel,        vanadium, iron, manganese, molybdenum or tungsten    -   d.) 0.5 to 30% by weight of at least one water-soluble or        water-dispersible film-forming organic polymer or copolymer        (based on active substance)    -   e.) 0.1 to 10% by weight of an organophosphonic acid    -   f.) optionally other auxiliaries and additives.

It is clear in many cases from the documents cited above that theconversion layers produced are colorless and transparent, so that thetreated metal surfaces have a bright metallic appearance. At least it isnot disclosed in those documents that colored layers would be formed.The lack of color in the prior art coatings is a drawback where, frommany years' experience in the chromating of metal surfaces, the expertin this field is accustomed to obtaining a colored layer as the outcomeof the conversion treatment. One is then immediately able to see whetherthe treatment has produced the desired result. In the production ofcolorless layers, however, this involves complicated surface analysis,for example determining the Ti or Zr content of the surface by X-rayfluorescence measurement. Accordingly, there is a need in practice forsurface treatment processes which not only are comparable withconventional chromating layers in their properties in regard tocorrosion prevention and paint adhesion, but are also visible to thehuman eye in the same way as chromating layers.

Proposals for solving this problem exist in the prior art. For example,WO 94/256450 describes a process for producing blue-colored conversionlayers on zinc/aluminium alloys. In this process, the metal surfaces arecontacted with a treatment solution which has a pH of 3.5 to 6 and whichcontains 0.2 to 3.0% by weight molybdenum and 0.1 to 2.0% by weightfluoride. The molybdenum may be used as molybdate, as phosphomolybdicacid, as molybdenum chloride and the like. The fluoride may be used inthe form of hydrofluoric acid, simple fluorides and complex fluoroacids, such as fluorotitanic acid or fluorozirconic acid for example.

The teaching of WO 00/26437 goes the way of coloring the conversionlayer with an organic dye (alizerin dye). The conversion layer itself isproduced with a treatment solution containing complex fluorides, forexample of titanium and zirconium, besides other inorganic oxides,hydroxides or carbonates or reaction products thereof with the fluoroacids. A poly-4-hydroxystyrene substituted by amino groups (polyvinylphenol) may additionally be used as an organic polymer.

FR 2 461 764 proposes the chemical oxidation of the aluminium surfacewith organic nitro compounds in alkaline solution. After the oxidationstep, the layers may be colored with an organic dye. A similar two-stepprocess is proposed in WO 01/71060. This document describes a multilayercoating of a conversion layer (obtainable, for example,electrochemically and having pores) applied to the metal and a coloredlayer on the conversion layer. The second colored layer may be obtainedby contact with a solution containing at least one alkoxysilane compoundand a dye, followed by polymerization and/or crosslinking of thealkoxysilane compound.

The processes cited above for producing chromium-free colored conversionlayers on metals, such as aluminium for example, may be divided into twogroups. In the first group, transition metal compounds, such asmolybdates or polymolybdates for example, or organic dyes areincorporated in the conversion layer. In the second group, a conversionlayer is conventionally produced and the organic dyes are applied to theconversion layer already formed in a second step. There appears to be noexample of a conversion treatment of metal surfaces carried out in thepresence of an organic polymer which, on the one hand, improves thecorrosion-inhibiting effect and paint adhesion of the conversion layerand which, on the other hand, carries color-bearing substituents, sothat the presence of this polymer on the metal surface can be detectedwith the eye.

In the treatment of circulating waters, for example of industrialcooling systems, it is known that organic polymers can be added toprevent corrosion or deposits. In this case, the problem arises ofmonitoring the concentration of these polymers in the circuit water. Tothis end, EP 504 520 proposes covalently bonding dye residues to theorganic polymers used for this purpose, so that the concentration of thepolymers in the circuit water can readily be determined by an absorptionor fluorescence measurement. This document discloses a number of organicdye residues and monomers which can be reacted with one another andpolymerized to obtain polymers containing color-bearing groups. Forexample, these polymers may contain one or more of the followingmonomers: acrylic acid, acrylamide, sulfomethacrylamide, vinyl acetate,methacrylic acid or acrylonitrile.

BRIEF SUMMARY OF THE INVENTION

The problem addressed by the present invention was to providecompositions and processes for producing chromium-free conversion layerson metal surfaces, conversion layers appearing colored to the human eyeor visibly fluorescing being produced in a single step. The dye usedwould not be independent of the actual active conversion componentsbecause, otherwise, it could not be guaranteed that the intensity of thecoloring or fluorescence would correlate with the thickness of theconversion layer. In Applicants' invention, the coloring agent iscovalently bonded to the polymer forming the conversion layer and hencethe color of the coating is directly related to the amount of thecoating, e.g. the thickness of the coating, on the substrate.

This problem has been solved by a chromium-free treatment solution forproducing colored or fluorescing corrosion prevention layers on metalsurfaces which contains:

-   -   a) phosphoric acid and/or at least one fluoro acid of one or        more elements from the group consisting of B, Si, Ti, Zr and Hf        or anions thereof and    -   b) at least one organic polymer, the organic polymer being        capable of binding to the metal surface through oxygen and/or        nitrogen atoms,        characterized in that the organic polymer carries covalently        bonded groups which appear colored to the human eye or which        fluoresce discernibly to the human eye on exposure to UV light.

In one embodiment, the invention provides a treatment solution forproducing colored corrosion prevention layers on metal surfaces whichcomprises:

a) phosphoric acid and/or at least one fluoro acid of one or moreelements selected from the group consisting of B, Si, Ti, Zr and Hf oranions thereof; and

b) at least one organic polymer capable of binding to a metal surfacethrough oxygen and/or nitrogen atoms and selected from the groupconsisting of amino resins, phenol/aldehyde resins, polymers containingcarboxyl groups, polymeric alcohols, esterification products ofpolymeric alcohols with polymers containing carboxylic acid groups,polymers containing amino groups, homo- or copolymers of vinylpyrrolidone, and copolymers of alkylene phosphonic or alkylenephosphinic acids and one or more unsaturated carboxylic acids, whereinthe treatment solution is chromium-free and the organic polymer carriescovalently bonded groups which appear colored to the human eye.

Desirably the treatment solution comprises 0.02 to 20 g/l phosphoricacid and/or at least one fluoro acid of one or more elements from thegroup consisting of B, Si, Ti, Zr and Hf or anions thereof and 0.1 to200 g/l of the organic polymer.

In another embodiment the treatment solution comprises: a) phosphoricacid present in a concentration of at least 1 g/l; and b) organicpolymer present in a concentration of at least 5 g/l and not more than150 g/l.

Desirably the percentage by weight of covalently bonded groups whichappear colored to the human eye amounts to 0.1 to 20% by weight, basedon the total weight of the organic polymer. In one embodiment, thecovalently bonded groups which appear colored to the human eye areselected from Toluidine Blue and Neutral Red.

In one embodiment, the organic polymer has an upper molecular weightlimit of 20,000,000 Dalton and an average molecular weight of greaterthan 100,000 Dalton.

In a preferred embodiment the organic polymer is selected from the groupconsisting of polymers of acrylate and/or methacrylate monomers, maleicanhydride which may be completely or partly hydrolyzed, and acrylate ormethacrylate monomers terminated by phosphate groups.

Desirably the treatment solution may contain d) at least one inorganiccompound in particle form with a mean particle diameter in the rangefrom 0.005 to 0.2 μm; the inorganic compound in particle form may bepresent in the aqueous bath solution in a concentration of 0.1 to 80g/l.

In one embodiment of the treatment solution, the organic polymer is acopolymer of a) acrylic acid and/or methacrylic acid with b) acrylateand/or methacrylate monomers terminated by phosphate groups whichcontains covalently bonded molecules of Toluidine Blue or Neutral Red.

In a one embodiment, the treatment solution comprises at least 0.025 g/land up to 10 g/l Ti and/or Zr and/or Si ions and at least such aquantity of fluoride that the atomic ratio of Ti to F and/or Zr to Fand/or Si to F is in the range from 1:1 to 1:6. The treatment solutionmay comprise both fluoro acids of Ti and of Zr, wherein the molar ratioof Ti to Zr is in the range from 10:1 to 1:10.

In another aspect of the invention, it is an object to provide a processfor producing colored or fluorescent corrosion prevention layers onmetal surfaces, comprising contacting the metal surfaces for 0.5 to 10minutes with the treatment solution as described and/or claimed hereinwhich has a temperature of 20 to 80° C. In one embodiment, the metalsurfaces treated are selected from surfaces of aluminium and aluminiumalloys, magnesium and magnesium alloys, titanium and titanium alloys,zinc and zinc alloys, galvanized and alloy-galvanized steel.

In yet another aspect of the invention, it is an object to provide ametal part having at least one surface comprising a colored corrosionprevention layer produced according to the process described and/orclaimed herein.

Another embodiment of the invention provides a treatment solution forproducing colored corrosion prevention layers on metal surfaces whichcomprises:

a) 0.02 to 20 g/l phosphoric acid and/or at least one fluoro acid of oneor more elements from the group consisting of B, Si, Ti, Zr and Hf oranions thereof and

b) 0.1 to 200 g/l of at least one organic polymer capable of binding toa metal surface through oxygen and/or nitrogen atoms and selected fromthe group consisting of maleic anhydride/methyl vinyl ether copolymerand acrylic acid and methacrylate monomer terminated by phosphategroups; wherein the treatment solution is chromium-free and the organicpolymer carries 0.1 to 20% by weight, based on the total weight of theorganic polymer, of covalently bonded groups which appear colored to thehuman eye.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a treatment solution for producing coloredcorrosion prevention layers on metal surfaces which comprises:

a) phosphoric acid and/or at least one fluoro acid of one or moreelements selected from the group consisting of B, Si, Ti, Zr and Hf oranions thereof; and

b) at least one organic polymer capable of binding to a metal surfacethrough oxygen and/or nitrogen atoms and selected from the groupconsisting of amino resins, phenol/aldehyde resins, polymers containingcarboxyl groups, polymeric alcohols, esterification products ofpolymeric alcohols with polymers containing carboxylic acid groups,polymers containing amino groups, homo- or copolymers of vinylpyrrolidone, and copolymers of alkylene phosphonic or alkylenephosphinic acids and one or more unsaturated carboxylic acids, whereinthe treatment solution is chromium-free and the organic polymer carriescovalently bonded groups which appear colored to the human eye.

The treatment solution is, by definition, free from chromium, i.e. doesnot contain any intentionally added chromium compounds. However, tracesof chromium as impurities cannot be ruled out, for example as a resultof being dissolved out from the tank material. In addition, itpreferably does not contain any other heavy metal ions than those ofcomponent a). This reduces the demands on the treatment of thewastewaters accumulating.

In particular, the treatment solution is not intended to deposit acomplete layer-forming phosphate coating. The solution does not containmore than 3 g/l phosphoric acid and more than 0.3 g/l zinc and/ormanganese ions at one and the same time. The deposition of zinc and/ormanganese phosphate crystals on the metal surface is avoided in thisway. This would correspond to a more or less complete layer-formingphosphating which is unwanted in the context of the present invention.

A preferred treatment solution is characterized in that it contains

-   -   a) 0.02 to 20 g/l phosphoric acid and/or at least one fluoro        acid of one or more elements from the group consisting of B, Si,        Ti, Zr and Hf or anions thereof and    -   b) 0.1 to 200 g/l of the organic polymer.

If the treatment solution contains phosphoric acid, its minimumconcentration is preferably at least 1 g/l and, more particularly, atleast 5 g/l. An upper concentration limit of 15 g/l is generallysufficient.

If the treatment solution contains a fluoro acid of boron, for exampletetrafluoroboric acid, as component a), its concentration is preferablyselected so that the treatment solution contains at least 0.01 g/l,preferably at least 0.02 g/l and up to 5 g/l, preferably up to 1 g/l andmore particularly up to 0.5 g/l boron (expressed as element). If itcontains fluoro acids of hafnium, for example as hexafluoro acid, itsconcentration is preferably selected so that the treatment solutioncontains at least 0.02 g/l, preferably at least 0.5 g/l and up to 10g/l, preferably up to 5 g/l and more particularly up to 1 g/l hafnium.

Particularly preferred treatment solutions contain fluoro acids of Si,Ti and/or Zr as component a). A treatment solution is preferably usedwhich contains in all at least 0.01 g/l, preferably at least 0.025 g/land up to 10 g/l, preferably up to 1 g/l and more particularly up to 0.5g/l Ti and/or Zr and/or Si ions and at least such a quantity of fluoridethat the atomic ratio of Ti to F and/or Zr to F and/or Si to F is in therange from 1:1 to 1:6. The Ti, Zr and/or Si ions mentioned may becompletely used in the form of hexafluoro complexes such as, forexample, the hexafluoro acids or their salts soluble in water in theconcentration range mentioned, such as the sodium salts for example. Inthis case, the atomic ratio is 1:6. However, complex compounds whereless than six fluoride ions are attached to the central elements Ti, Zror Si may also be used. These may be spontaneously formed in thetreatment solution if both hexafluoro complexes of at least one of thecentral elements Ti, Zr or Si and at least one other compound of one ofthese central elements are added to the treatment solution. Suitableother compounds are, for example, nitrates, carbonates, hydroxidesand/or oxides of the same central element or of another of the threecentral elements mentioned. For example, the treatment solution maycontain hexafluorozirconate ions and (preferably colloidal) silica(SiO₂) or reaction products thereof. Unreacted silica may be suspendedin the treatment solution. A treatment solution such as this may also beobtained by using hydrofluoric acid or (optionally acidic) salts thereoftogether with compounds of Ti, Zr and/or Si which are capable of formingfluoro complexes therewith. Examples are the already mentioned nitrates,carbonates, hydroxides and/or oxides. A preferred embodiment ischaracterized in that, in all, such a quantity of Ti, Zr and/or Si asthe central metal and such a quantity of fluoride are used that theatomic ratio of central metal to fluoride is 1:2 or lower, moreparticularly 1:3 or lower. The atomic ratio may even be lower than 1:6if the treatment solution contains more fluoride, for example in theform of hydrofluoric acid or salts thereof, than is stoichiometricallynecessary for forming the hexafluoro complexes of the central metals Ti,Zr and/or Si. For example, the atomic ratio may be as low as 1:12 or1:18 or even lower if a corresponding excess of fluoride is used, i.e.two, three or even more times the quantity required for completeformation of the hexafluoro complexes.

Treatment solutions containing fluoro acids of Ti and/or Zr areparticularly preferred. It can be particularly beneficial to thecorrosion-inhibiting effect if the treatment solution contains bothfluoro acids of Ti and of Zr. In this case, the molar ratio of Ti to Zrmay be in the range from 10:1 to 1:10 and, more particularly, is in therange from 2:1 to 1:2.

The pH of the treatment solution should not be significantly below avalue of 1 because lower pH values lead to an increasingly strongercorrosive attack on the metal surface. The pH is preferably no lowerthan 2 and, more particularly, no lower than 2.5. At pH values above 6,the conversion layer is no longer formed to the desired extent. Thetreatment is preferably carried out at pH values no higher than 4 and,more particularly, no higher than 3.5.

The essential components a) and optionally b) mentioned are allprotolytes, i.e. molecules or ions which are capable of entering into anacid/base reaction in which protons are released or taken up.Accordingly, it is clear to the expert that these components enter intosuch reactions with one another and with the solvent, water, until thecorresponding chemical equilibria are reached. In the pH rangementioned, all these protolytes can be expected to be present in apartly proteolyzed state, irrespective of whether they have beenintroduced into the treatment solution in the form of their acids ortheir salts. The pH values mentioned, which are in the acidic range, arepreferably established by introducing the phosphoric acid and/or complexfluoro acids in the form of the free acids. There is therefore no needfor an additional acid for establishing the acidic pH value. However,these complex fluoride ions or phosphoric acid could even be used in theform of their salts and the desired pH value could be established byaddition of another acid, such as nitric acid for example. Alkalis, suchas NaOH or ammonia for example, are suitable for raising the pH value ifnecessary.

The concentration of the organic polymer b) in the treatment solution ispreferably in the range from 0.1 to 200 g/l. The particularly preferredminimum concentration is—with increasing preference—at least 1 g/l, atleast 5 g/l, at least 10 g/l, at least 15 g/l. The upper concentrationlimit is—with increasing preference—150 g/l, 100 g/l, 70 g/l.

So far as the concentrations of the active components a) and b) areconcerned, it may generally be said that the quality of the layergradually diminishes if the concentration falls below the minimum valuementioned. Any increase in concentration beyond the maximum mentioned isnot normally harmful, but does not afford any significant advantages andis therefore uneconomical.

In the organic polymer b), the percentage by weight of covalently bondedgroups which appear colored to the human eye or which fluoresce visiblyto the human eye on exposure to UV light is at least 0.1, preferably atleast 0.5 and more particularly at least 1% by weight and up to 20,preferably up to 15 and more particularly up to 10% by weight, based onthe total weight of the organic polymer.

The organic polymer b) may be selected from various groups. The organicpolymer is preferably selected from epoxy resins, amino resins,phenol/aldehyde resins, polymers containing carboxylic acid groups,polymeric alcohols, esterification products of polymeric alcohols withpolymers containing carboxylic acid groups, polymers containing aminogroups, homo- or copolymers of vinyl pyrrolidone and from polymerscontaining phosphinic acid, phosphonic acid or phosphoric acid estergroups.

In the case of phenol/aldehyde resins, formaldehyde resins arepreferred. Particularly suitable polymers containing amino groups areamino-substituted poly-4-vinylphenol compounds. Examples of suchpoly-4-vinylphenol compounds without covalently bonded color-bearinggroups can be found in the WO 00/26437 cited above and the literaturecited therein and, more particularly, in U.S. Pat. No. 5,281,282.

In addition, the organic polymers b) may be selected in regard to theirpolymeric backbone from:

-   -   e) polyvinyl alcohol or water-soluble or water-dispersible        partial esters thereof,    -   f) polymers or copolymers of unsaturated mono- or dicarboxylic        acid esters or amides thereof    -   g) esters of the group e) and group f) polymers,    -   h) polymers or copolymers of vinyl pyrrolidone,    -   i) polymers of diglycidyl ether of bisphenol A,    -   k) copolymers of alkylene phosphonic or alkylene phosphinic        acids and one or more unsaturated carboxylic acids.

Referring to the group e) polymer, the expression “partial ester” meansthat the alcohol groups are only partly esterified, the ester beingformed with non-polymeric carboxylic acids. In particular, theesterification may be carried out with monobasic C₁₋₄ carboxylic acids.

The group f) polymers or copolymers may be selected, for example, fromhomo- or copolymers of acrylic acid and/or methacrylic acid of which theacid groups may be partly replaced by amide groups or esterified withalcohols, more particularly with simple C₁₋₄ alcohols. Special examplesare homopolymers or copolymers of or with methyl methacrylate, n-butylacrylate, hydroxyethyl acrylate and glycerol propoxytriacrylate. Thesespecial examples are known, for example, from WO 95/14117. In addition,the group f) polymers may be selected from polymers containing maleicacid monomers. A special example of this is a maleic acid/methyl vinylether copolymer.

Group e) polymers generally contain free alcohol groups while group f)polymers generally contain free carboxylic acid groups. Accordingly,these two polymers may not only be used in admixture with one another,but also in a form in which at least partial esterification has takenplace between the alcohol groups of polymer e) and the carboxylic acidgroups of polymer f). This is explained in more detail in WO 94/12570.The teaching described therein may also be used for the purposes of thepresent invention.

In addition, the treatment solution may contain group h) polymers. Suchpolymers and their use in conversion treatment solutions are describedin detail in DE-A-100 05 113 and in DE-A-101 31 723.

The additional polymers may also be selected from those of group i), asdescribed in more detail in U.S. Pat. No. 5,356,490.

Particularly preferred polymers are organic polymers b) which areselected in regard to their polymeric backbone from polymers orcopolymers of acrylate and/or methacrylate monomers, maleic anhydridewhich may be completely or partly hydrolyzed (more particularly methylvinyl ether/maleic anhydride copolymers) and acrylate or methacrylatemonomers terminated by phosphate groups. Special examples of this can befound in the experimental section of this application.

The covalently bonded groups in the organic polymer b), which appearcolored to the human eye or which fluoresce discernibly to the human eyeon exposure to UV light, are preferably selected from Toluidine Blue(CAS No. 92-31-9), whose chemical name is3-amino-7-(dimethylamino)-2-methylphenothiazin-5-ium chloride, and fromNeutral Red (CAS No. 553-24-2), whose chemical name is3-amino-7-(dimethylamino)-2-methyl phenazine.

The average molecular weight of the organic polymers a) is preferably atleast 10,000 Dalton. The upper molecular weight limit is not critical aslong as the polymer is soluble or dispersible in the desiredconcentration range in the preferably acidic treatment solution. Forexample, the upper molecular weight limit can be 50,000,000, preferably20,000,000 and more particularly 10,000,000 Dalton. An upper limit of5,000,000 Dalton can also be sufficient. The average molecular weight ispreferably above 50,000 Dalton and more particularly above 100,000Dalton. The average molecular weights can be determined, for example, bygel permeation chromatography with polyethylene glycol as standard.

In a particularly preferred embodiment, the organic polymer b) is acopolymer of i) acrylic acid and/or methacrylic acid with ii) acrylateand/or methacrylate monomers terminated by phosphate groups, thecopolymer containing covalently bonded molecules of Toluidine Blue orNeutral Red. The production of this polymer is described by way ofexample in Examples 3 and 10. These polymers are examples of polymerswhich contain both carboxylate and phosphonic acid groups or phosphoricacid ester groups. By virtue of their particularly high affinity formetal surfaces, these polymers with their various polar adhesion groupsare particularly preferred. These particularly preferred copolymers canalso be obtained, for example, by reaction of acrylic acid and/ormethacrylic acid with other unsaturated phosphonic acids, phosphinicacids or phosphoric acid esters. For example, vinyl phosphonic acid maybe used as an unsaturated monomer containing a phosphonic acid group.

Applicants were unable to find any prior-art document which describedthe particularly preferred copolymer of i) acrylic acid and/ormethacrylic acid with ii) acrylate and/or methacrylate monomersterminated by phosphate groups which contains covalently bondedmolecules of Toluidine Blue or Neutral Red. Accordingly, the presentinvention also relates to this copolymer itself. The foregoingobservations again apply in regard to the preferred molecular weights.Similarly, the foregoing observations on the percentage by weight of dyegroups, based on the total weight of the polymer, again apply. The ratioby weight between monomers i) and ii) is preferably in the range from10:1 to 1:10, more preferably in the range from 5:1 to 1:5 and mostpreferably in the range from 3:1 to 1:3.

Another preferred polymer for the treatment solution according to theinvention is a methyl vinyl ether/maleic anhydride copolymer to whichmolecules of Toludine Blue or Neutral Red are covalently bonded and ofwhich the anhydride groups are at least partly hydrolyzed, preferably atleast 90% hydrolyzed. The molar ratio of the monomeric methyl vinylether and maleic anhydride is preferably in the range from 10:1 to 1:10,more preferably in the range from 5:1 to 1:5 and most preferably in therange from 1:2 to 2:1. For example, the molar ratio can be substantially1:1.

In addition, the aqueous treatment solution may contain as an additionalcomponent i) a total of 1 to 2,000 mg/l of one or more chelatingcomplexing agents which do not come under the definition of the organicpolymers of group b). The chelating complexing agent c) is preferablynot polymeric and is preferably selected from molecules containing twoor more phosphonic acid groups, more particularly from geminaldiphosphonic acids and phosphonocarboxylic acids and anions thereof. (Asexplained above, the corresponding acid/base equilibrium between theacid form and the salt form of the complexing agent is established byitself in the treatment solution and in the concentrate, depending onthe pH value, irrespective of the form in which it was introduced intothe solution or the concentrate.)

Examples of such complexing agents are those which may also be used inaccordance with DE-A-103 39 165 to which reference is hereby made.

The properties of the conversion layer obtained may be further improvedwhere necessary if the treatment solution (irrespective of whether ornot component c) is also present) contains an inorganic compound inparticle form with a mean particle diameter, as measured with a scanningelectron microscope, of 0.005 to 0.2 μm as an additional component d).

The inorganic compound in particle form is present in the aqueous bathsolution in a concentration of 0.1 to 80 g/l, preferably in aconcentration of 0.2 to 25 g/l, more preferably in a concentration of0.5 to 10 g/l and most preferably in a concentration of 1 to 4 g/l.

The ratio of the contents of organic polymer b) to the contents ofinorganic compounds in particle form in the aqueous bath solution mayvary within wide limits and, in one particular embodiment, may be<3.8:1. This ratio is preferably in the range from 0.05:1 to 3.5:1 andmore particularly in the range from 0.18:1 to 2.5:1.

In the process according to the invention, a fine-particle powder, adispersion or a suspension, such as for example a carbonate, an oxide, asilicate or a sulphate, more particularly colloidal or amorphousparticles, is added as the inorganic compound in particle form.Particles based on at least one compound of aluminium, barium, cerium,calcium, lanthanum, silicon, titanium, yttrium, zinc and/or zirconiumand especially particles based on aluminium oxide, barium sulphate,cerium dioxide, rare earth mixed oxide, silicon dioxide, silicate,titanium oxide, yttrium oxide, zinc oxide and/or zirconium oxide areparticularly preferred as the inorganic compound in particle form. Theat least one inorganic compound in particle form is present in the formof particles with a mean particle size of preferably 6 nm to 150 nm,more preferably 7 to 120 nm, most preferably 8 to 90 nm and, in one evenmore preferred embodiment, 8 to 60 nm up to 25 nm. Relatively largeparticles preferably have a platelet-like or elongate shape.

In cases where metallic substrates coated in accordance with theinvention and optionally provided with paint or paint-like coatings areto be welded, it can be of advantage to use particles of relatively highor high electrical conductivity as the particles of the compound inparticle form, more particularly particles of oxides, phosphates,phosphides or sulphides of aluminium, iron or molybdenum, moreparticularly aluminium phosphide or iron oxide, iron phosphide, at leastone molybdenum compound, such as molybdenum sulphide, graphite and/orcarbon black. These particles may even have such an average particlesize that they may project slightly further out from the layer producedin accordance with the invention

The present invention also relates to a process for producing colored orfluorescent corrosion prevention layers on metal surfaces, characterizedin that the metal surfaces are contacted for 0.5 to 10 minutes with thetreatment solution claimed in one or more of claims 1 to 8 which has atemperature of 20 to 80° C.

The metal surface may be contacted with the treatment solution bystandard methods such as, for example, immersion, spraying, acombination of spraying and immersion, roller application, etc. Aftercontact with the treatment solution, the metal surfaces are preferablyrinsed with water, more particularly with deionized water, and thendried by standard methods. The contact time is preferably at least 1minute, more particularly at least 2 minutes. A contact time of up to 7minutes, for example up to 5 minutes, is generally sufficient.

A no-rinse treatment, i.e. application (by roller, spraying andsqueezing) without rinsing, is also possible. The temperature of thetreatment solution is preferably at least 30° C., for example 35° C. Thetemperature of the treatment solution generally need not exceed an upperlimit of 60° C. and more particularly 50° C.

The metal surfaces which can be treated by the process according to theinvention are preferably selected from surfaces of aluminium andaluminium alloys, magnesium and magnesium alloys, titanium and titaniumalloys, zinc and zinc alloys, galvanized or alloy-galvanized steel. Themetal surfaces may be surfaces of the above-mentioned metals or theiralloys as such or even surfaces of a substrate such as, for example,steel coated with the above-mentioned metals or their alloys. Examplesof the latter are electrolytically galvanized or hot-dip-galvanizedsteel, aluminized steel or coated steels, such as Galvalume® or Galfan®,which carry a coating of zinc/aluminium alloys.

Finally, the present invention relates to a metal part of which thesurface has a colored or fluorescent corrosion prevention layerobtainable by the process according to the invention. The foregoingobservations on the particularly preferred metals apply accordingly. Themetal part may carry the colored or fluorescent corrosion preventionlayer obtainable by the process according to the invention as a singlecoating or as an outermost coating. However, the process according tothe invention generally serves as a pretreatment for another coating,for example a coating with a paint or even with an adhesive if thetreated metal parts are to be bonded to one another or to othersubstrates. Accordingly, the metal part according to the invention mayhave a paint as the outermost layer or may be bonded to another metalpart according to the invention or even to another substrate.

The treatment step according to the invention is generally part of atreatment sequence such as typically applied in the conversion treatmentof the above-mentioned metal surfaces before subsequent coating orbonding. A corresponding process sequence generally begins withcleaning/degreasing of the metal surfaces, for which an alkalinecleaner, for example, can be used. This is followed by one or morerinsing steps with water. These in turn are followed by an acidictreatment step for removing surface oxides that were not removed in thealkaline cleaning step. This step is also known as “deoxidizing” or“scouring” and is applied in particular to surfaces of aluminium and itsalloys. After an intermediate rinse with water and preferably anadditional rinse with deionized water, the treatment step according tothe invention is carried out with the treatment solution according tothe invention. This may be followed by another rinse with water.However, the process may also be carried out as a no-rinse process, i.e.there is no need for rinsing with water after the treatment stepaccording to the invention.

The outcome of this treatment sequence is a colored or fluorescent,corrosion-protected metal surface which shows good adhesion to asubsequently applied layer based on organic polymers, for example apaint or an adhesive. This surface generally contains 1 to 70 mgtitanium and/or zirconium per m² and more particularly 3 to 30 mg/m²where the fluoro acids of these metals were used as component a). Thesevalues may be measured by standard surface analysis techniques, forexample by X-ray fluorescence methods.

Accordingly, the process according to the invention provides metalsurfaces characterized by good corrosion protection and good paintadhesion which the expert knows to be the outcome of the technicallyhighly advantageous, but ecologically and physiologically unsafechromating processes. By virtue of the coloring of the surface, theexpert is able immediately to see whether an adequate conversionlayer—to which he is accustomed from chromating—has been formed duringthe treatment. Accordingly, the process according to the invention hasthe technical advantage over the formation of colorless conversionlayers that the outcome of the treatment is immediately visible withoutany need for special surface analysis.

EXAMPLES

Preparing the Composition

Example 1 Production of a Toluidine Blue Monomer

3 g Toluidine Blue (CAS No. 92-31-9) were dissolved in 50 ml water andmixed with 200 ml pyridine. 1.1 g methacrylic acid chloride were addeddropwise to the solution while cooling with ice, followed by stirringfor one hour and 3 hours at 40° C. The solvent was distilled off invacuo. 3.8 g of the crude product were obtained.

Example 2 Production of a Neutral Red Monomer

3 g Neutral Red (CAS No. 553-24-2) were dissolved in 50 ml water andmixed with 200 ml pyridine. 1.1 g methacrylic acid chloride were addeddropwise to the solution while cooling with ice, followed by stirringfor one hour and 3 hours at 40° C. The solvent was distilled off invacuo. 3.7 g of the crude product were obtained.

Example 3 Polymerization I

0.2 g Toluidine Blue monomer, 13.8 g acrylic acid and 6 g methacrylatemonomer terminated by phosphate groups (Sipomer PAM 100, a product ofRhodia) were dissolved in 300 ml water and freed from oxygen byintroduction of nitrogen for 30 mins. at 50° C. The polymerization wasthen started by addition of 0.1 g V-44 (initiator). The solution wasstirred for 24 hours at 50° C. and polymerization was restarted withanother 0.1 g V-44 and continued for another 24 hours. Polymerizationwas restarted by adding 0.1 g V-50 (initiator), increasing the reactiontemperature to 80° C. and stirring for another 4 hours. The coloredpolymer solution was dialyzed for 48 hours (dialysis tube with a cutofflimit of 10,000 Dalton). After dialysis, 670 ml of a 2.4% by weight ofcovalently bonded groups, colored solution were obtained, correspondingto a yield of 80%.

Example 4 Polymerization II

0.2 g Toluidine Blue monomer, 13.8 g acrylic acid and 6 g vinylphosphonic acid were dissolved in 300 ml water and freed from oxygen byintroduction of nitrogen for 30 mins. at 50° C. The polymerization wasthen started by addition of 0.1 g V-44 (initiator). The solution wasstirred for 24 hours at 50° C. and polymerization was restarted withanother 0.1 g V-44 and continued for another 24 hours. Polymerizationwas restarted by adding 0.1 g V-50 (initiator), increasing the reactiontemperature to 80° C. and stirring for another 4 hours. The coloredpolymer solution was dialyzed for 48 hours (dialysis tube with a cutofflimit of 10,000 Dalton). After dialysis, 470 ml of a 3% by weight ofcovalently bonded groups, colored solution were obtained, correspondingto a yield of 70%. An average molecular weight M_(w) of 45,000 wasdetermined by gel permeation chromatography. The GPC column wascalibrated with a polyacrylate standard.

Example 5 Reaction of Toluidine Blue with Methyl Vinyl Ether/MaleicAnhydride Copolymers

0.1 g Toluidine Blue were dissolved in 300 ml of a water/ice mixture. 10g maleic anhydride/methyl vinyl ether copolymer (Gantrez AN-119, aproduct of GAF General Aniline Firm Corp.) (M_(w)=216,000 g/mol) werethen added with vigorous stirring, followed by stirring for 24 hours.For complete hydrolysis of the anhydride groups, the solution was heatedfor 2 hours to 80° C. To remove the unreacted dye molecules, thesolution was dialyzed for 48 hours (dialysis tube with a cutoff limit of10,000 Dalton). After dialysis, 400 ml of a 0.31% by weight ofcovalently bonded groups, colored solution were obtained.

Example 6 Reaction of Toluidine Blue with Methyl Vinyl Ether/MaleicAnhydride Copolymers

0.1 g Toluidine Blue were dissolved in 380 ml of a water/ice mixture. 10g maleic anhydride/methyl vinyl ether copolymer (Gantrez AN-139, aproduct of GAF General Aniline Firm Corp.) (M_(w)=1,080,000 g/mol) werethen added with vigorous stirring, followed by stirring for 24 hours.For complete hydrolysis of the anhydride groups, the solution was heatedfor 2 hours to 80° C. To remove the unreacted dye molecules, thesolution was dialyzed for 48 hours (dialysis tube with a cutoff limit of10,000 Dalton). After dialysis, 400 ml of a 2.34% by weight ofcovalently bonded groups, colored solution were obtained.

Example 7 Reaction of Toluidine Blue with Methyl Vinyl Ether/MaleicAnhydride Copolymers

0.1 g Toluidine Blue were dissolved in 300 ml of a water/ice mixture. 10g maleic anhydride/methyl vinyl ether copolymer (Gantrez AN-169, aproduct of GAF General Aniline Firm Corp.) (M_(w)=1,980,000 g/mol) werethen added with vigorous stirring, followed by stirring for 24 hours.For complete hydrolysis of the anhydride groups, the solution was heatedfor 2 hours to 80° C. To remove the unreacted dye molecules, thesolution was dialyzed for 48 hours (dialysis tube with a cutoff limit of10,000 Dalton). After dialysis, 400 ml of a 2.4% by weight of covalentlybonded groups, colored solution were obtained.

Example 8 Reaction of Toluidine Blue with Methyl Vinyl Ether/MaleicAnhydride Copolymers

0.4 g Toluidine Blue were dissolved in 300 ml of a water/ice mixture. 10g maleic anhydride/methyl vinyl ether copolymer (Gantrez AN-139, aproduct of GAF General Aniline Firm Corp.) (M_(w)=1,080,000 g/mol) werethen added with vigorous stirring, followed by stirring for 24 hours.For complete hydrolysis of the anhydride groups, the solution was heatedfor 2 hours to 80° C. To remove the unreacted dye molecules, thesolution was dialyzed for 48 hours (dialysis tube with a cutoff limit of10,000 Dalton). After dialysis, 400 ml of a 2.24% by weight ofcovalently bonded groups, colored solution were obtained.

Example 9 Reaction of Neutral Red with Methyl Vinyl Ether/MaleicAnhydride Copolymers

0.1 g Neutral Red were dissolved in 380 ml of a water/ice mixture. 10 gmaleic anhydride/methyl vinyl ether copolymer (Gantrez AN-139, a productof GAF General Aniline Firm Corp.) (M_(w)=1,080,000 g/mol) were thenadded with vigorous stirring, followed by stirring for 24 hours. Forcomplete hydrolysis of the anhydride groups, the solution was heated for2 hours to 80° C. To remove the unreacted dye molecules, the solutionwas dialyzed for 48 hours (dialysis tube with a cutoff limit of 10,000Dalton). After dialysis, 400 ml of a 2.1% by weight of covalently bondedgroups, colored solution were obtained.

Example 10 Polymerization III

0.2 g Neutral Red monomer, 13.8 g acrylic acid and 6 g methacrylatemonomer terminated by phosphate groups (Sipomer PAM 100, a product ofRhodia) were dissolved in 550 ml water and freed from oxygen byintroduction of nitrogen for 30 mins. at 50° C. The polymerization wasthen started by addition of 0.1 g V-44 (initiator). The solution wasstirred for 24 hours at 50° C. and polymerization was restarted withanother 0.1 g V-44 and continued for another 24 hours. Polymerizationwas restarted by adding 0.1 g V-50 (initiator), increasing the reactiontemperature to 80° C. and stirring for another 4 hours. The coloredpolymer solution was dialyzed for 48 hours (dialysis tube with a cutofflimit of 10,000 Dalton). After dialysis, 650 ml of a 2.39% by weight ofcovalently bonded groups, colored solution were obtained, correspondingto a yield of 77%.

Pretreatment of Aluminium Substrates with Chromium-Free Polymer Solution

Test plates of the aluminium alloy A199.5 were subjected to thefollowing standard pretreatment before the treatment step according tothe invention:

-   -   Cleaning: spraying with an alkaline cleaner (Ridoline® C 72, 2%,        a product of Henkel KGaA), 65° C., 1 minute    -   Rinsing: tap water, room temperature, 1 minute    -   Rinsing: deionized water, room temperature, 1 minute

This was followed by the treatment step according to the invention at pH2.7, carried out by dipping as described below.

After the conversion treatment step, the plates were dried at 60° C. ina recirculating air oven and then coated with a commercially availablepowder coating. A standard paint adhesion test was then carried out. Thetest plates were provided with a cross-hatch cut and then stored for 2hours in boiling deionized water and then for one hour at roomtemperature. An adhesive tape was then applied to the cross-hatched areaand peeled off. The amount of paint removed from the test plate wasevaluated and characterized by cross-hatch scores: Ch 0: no paint loss,Ch 5: extensive paint loss. In addition, paint creepage was tested bythe salt spray test.

The compositions of the treatment solutions and the treatment resultsare set out in the following:

Example 11

Composition of a 100 G Aqueous Treatment Solution: H₂TiF₆  0.1 g Polymer(Example 6) 2.55 g Water 97.35 gDipping of aluminium plates in pretreatment aftera) 2 mins.: plates assumed a light blue shimmer after dryingb) 5 mins.: plates assumed a clearly visible blue tone after drying

Example 12

Composition of a 100 g Aqueous Treatment Solution: H₂TiF₆  0.1 g Polymer(Example 6) 1 g Water 98.9 gDipping of aluminium plates in pretreatment aftera) 2 mins.: plates assumed a very light blue shimmer after dryingb) 5 mins.: plates assumed a very light blue shimmer after drying

Example 13

Composition of a 100 g Aqueous Treatment Solution: H₂TiF₆  0.1 g Polymer(Example 6) 1.25 g Water 98.65 gDipping of aluminium plates in pretreatment aftera) 2 mins.: plates assumed a light blue shimmer after dryingb) 5 mins.: plates assumed a light blue shimmer after drying

Example 14

Composition of a 100 g Aqueous Treatment Solution: H₂TiF₆  0.1 g Polymer(Example 7) 3.6 g Water 96.3 gDipping of aluminium plates in pretreatment aftera) 2 mins.: plates assumed a dark blue tone after dryingb) 5 mins.: plates assumed a dark blue tone after drying

Example 15

Composition of a 100 g Aqueous Treatment Solution: H₂TiF₆  0.1 g Polymer(Example 7) 1.8 g Water 98.1 gDipping of aluminium plates in pretreatment aftera) 2 mins.: plates assumed a clearly visible blue tone after dryingb) 5 mins.: plates assumed a clearly visible blue tone after drying

Example 16

Composition of a 100 g Aqueous Treatment Solution: H₂TiF₆ 0.1 g Polymer(Example 7) 0.9 g Water  99 gDipping of aluminium plates in pretreatment aftera) 2 mins.: plates did not assume a blue tone after dryingb) 5 mins.: plates assumed a very light blue shimmer after drying

Example 17

Composition of a 100 G Aqueous Treatment Solution: H₂TiF₆  0.1 g Polymer(Example 3) 3.53 g Water 96.37 gDipping of Aluminium Plates in Pretreatment aftera) 2 mins.: plates assumed a clearly visible blue tone after dryingb) 5 mins.: plates assumed a clearly visible blue tone after drying

Example 18

Composition of a 100 G Aqueous Treatment Solution: H₂TiF₆  0.1 g Polymer(Example 3) 1.8 g Water 98.1 gDipping of aluminium plates in pretreatment aftera) 2 mins.: plates assumed a very light blue shimmer after dryingb) 5 mins.: plates assumed a light blue shimmer after drying

Example 19

Composition of a 100 g Aqueous Treatment Solution: H₂TiF₆  0.1 g Polymer(Example 10) 3.53 9 Water 96.37 gDipping of aluminium plates in pretreatment aftera) 2 mins.: plates assumed a clearly visible red tone after dryingb) 5 mins.: plates assumed a clearly visible red tone after drying

Example 20

Composition of a 100 g Aqueous Treatment Solution: H₂TiF₆  0.1 g Polymer(Example 10) 1.8 g Water 98.1 gDipping of aluminium plates in pretreatment aftera) 2 mins.: plates assumed a very light pink shimmer after dryingb) 5 mins.: plates assumed a light pink shimmer after dryingCorrosion-Inhabiting Properties of Plates (Al 99.5 F 19) Pretreated andthen Painted in Accordance with the Invention:Cleaning/Rinsing with Water: as Above

The treatment solutions contained 1% by weight H₂TiF₆ and the quantityof polymer shown in Table 1. Temperature: 35° C. Treatment time, pH ofthe treatment solution and tests: see Table 1; test results: Tables 2and 3.

Drying: recirculating air drying cabinet, 60° C.

Paint: BASF standard, white

Powder coating, Ral 9010

Hardening: 20 mins., 360° C.

Paint thickness: see Tables 2 and 3

Corrosion Tests: See Tables TABLE 1 Treatment parameters, tests carriedout Identification of Exam- Plate Numbers on ple Appear- which ListedTests No. Polymer pH, time ance were Performed 21 Example 10 pH 2.7 PinkSalt spray test 3% Polymer 2 mins. uniform (DIN 50021 SS): (Plate No.:6, 7) Boiling test: (Plate No.: 8, 9) 22 Example 10 pH 3.3 Dark pinkSalt spray test 3% Polymer 2 mins. opalescent (DIN 50021 SS): uniform(Plate No.: 11, 12) Boiling test: (Plate No.: 13, 14) 23  Example 8 pH2.7 Blue Salt spray test 3% polymer 3 mins. Uneven (DIN 50021 SS):(Plate No.: 21, 23) Boiling test: (Plate No.: 24, 25) 24 Example 10 pH2.96  Light pink Salt spray test 1.5% polymer 2 mins. uniform (DIN 50021SS): (Plate No.: 30, 33) Boiling test: (Plate No.: 34, 35) 25  Example 8pH 3.3 Dark blue Salt spray test 3% polymer 3 mins. uniform (DIN 50021SS): (Plate No.: 37, 38) Boiling test: (Plate No.: 39, 40)

Table 2 recites the plate by plate results of the testing from Table 1.TABLE 2 Test results: salt spray mist test to DIN 50021 SS Plate No. 6 711 12 21 23 30 33 37 38 Paint 99 98 84 95 73 69 51 92 100 114 thickness(μm) Blister count 0(SO) 0(SO) 0(SO) 0(SO) 0(SO) 0(SO) 0(SO) 0(SO) 0(SO)0(SO) to DIN EN ISO 4628-2 after 21 days Creepage at 18.4 19 9.6 14.40.8 1.0 2.2 1.6 1.2 1.0 cut to DIN 53167 after 21 days (mm) Blistercount 0(SO) 0(SO) 0(SO) 0(SO) 0(SO) 0(SO) 0(SO) 0(SO) 0(SO) 0(SO) to DINEN ISO 4628-2 after 21 days Creepage at 15.4 15.7 1.5 1.4 2.7 2.1 1.81.6 cut to DIN 53167 after 21 days (mm)

TABLE 3 Test results from selected plates (cf. Table 1): boiling test indeionized water, 2 hours at 100° C. Plate No. 8 9 13 14 24 25 34 35 3940 Paint thickness (μm) 114 90 77 70 87 60 68 119 108 91 Cross hatchingto DIN EN ISO 0 2 0 0 0 0 0 0 0 0 2409 [GT] before boiling test Crosshatching to DIN EN ISO 0 0 0-4 0-3 0 0 0 0 0 0 2409 [GT] 1 hour afterboiling test

1. A treatment solution for producing colored corrosion preventionlayers on metal surfaces which comprises a) phosphoric acid and/or atleast one fluoro acid of one or more elements selected from the groupconsisting of B, Si, Ti, Zr and Hf or anions thereof; and b) at leastone organic polymer capable of binding to a metal surface through oxygenand/or nitrogen atoms and selected from the group consisting of aminoresins, phenol/aldehyde resins, polymers containing carboxyl groups,polymeric alcohols, esterification products of polymeric alcohols withpolymers containing carboxylic acid groups, polymers containing aminogroups, homo- or copolymers of vinyl pyrrolidone, and copolymers ofalkylene phosphonic or alkylene phosphinic acids and one or moreunsaturated carboxylic acids, wherein the treatment solution ischromium-free and the organic polymer carries covalently bonded groupswhich appear colored to the human eye.
 2. The treatment solution asclaimed in claim 1, comprising: a) 0.02 to 20 g/l phosphoric acid and/orat least one fluoro acid of one or more elements from the groupconsisting of B, Si, Ti, Zr and Hf or anions thereof and b) 0.1 to 200g/l of the organic polymer.
 3. The treatment solution as claimed inclaim 1, wherein: a) the phosphoric acid is present in a concentrationof at least 1 g/l; and b) the organic polymer is present in aconcentration of at least 5 g/l and not more than 150 g/l.
 4. Thetreatment solution as claimed in claim 1, wherein the organic polymerhas an upper molecular weight limit of 20,000,000 Dalton and an averagemolecular weight of greater than 100,000 Dalton.
 5. The treatmentsolution as claimed in claim 1, wherein the percentage by weight ofcovalently bonded groups which appear colored to the human eye amountsto 0.1 to 20% by weight, based on the total weight of the organicpolymer.
 6. The treatment solution as claimed in claim 1, wherein theorganic polymer is selected from the group consisting of polymers ofacrylate and/or methacrylate monomers, maleic anhydride which may becompletely or partly hydrolyzed, and acrylate or methacrylate monomersterminated by phosphate groups.
 7. The treatment solution as claimed inclaim 1, wherein the covalently bonded groups which appear colored tothe human eye are selected from Toluidine Blue and Neutral Red.
 8. Thetreatment solution as claimed in claim 1, further comprising: d) atleast one inorganic compound in particle form with a mean particlediameter in the range from 0.005 to 0.2 μm.
 9. The treatment solution asclaimed in claim 1, wherein the inorganic compound in particle form ispresent in the aqueous bath solution in a concentration of 0.1 to 80g/l.
 10. The treatment solution as claimed in claim 1, wherein theorganic polymer is a copolymer of a) acrylic acid and/or methacrylicacid with b) acrylate and/or methacrylate monomers terminated byphosphate groups which contains covalently bonded molecules of ToluidineBlue or Neutral Red.
 11. The treatment solution as claimed in claim 1,comprising at least 0.025 g/l and up to 10 g/l Ti and/or Zr and/or Siions and at least such a quantity of fluoride that the atomic ratio ofTi to F and/or Zr to F and/or Si to F is in the range from 1:1 to 1:6.12. The treatment solution as claimed in claim 1, comprising both fluoroacids of Ti and of Zr, wherein the molar ratio of Ti to Zr is in therange from 10:1 to 1:10.
 13. A process for producing colored orfluorescent corrosion prevention layers on metal surfaces, comprisingcontacting the metal surfaces for 0.5 to 10 minutes with the treatmentsolution claimed in claim 1 which has a temperature of 20 to 80° C. 14.The process as claimed in claim 9, wherein the metal surfaces areselected from surfaces of aluminium and aluminium alloys, magnesium andmagnesium alloys, titanium and titanium alloys, zinc and zinc alloys,galvanized and alloy-galvanized steel.
 15. A metal part comprising atleast one surface comprising a colored corrosion prevention layerproduced according to the process claimed in claim
 9. 16. A treatmentsolution for producing colored corrosion prevention layers on metalsurfaces which comprises a) 0.02 to 20 g/l phosphoric acid and/or atleast one fluoro acid of one or more elements from the group consistingof B, Si, Ti, Zr and Hf or anions thereof and b) 0.1 to 200 g/l of atleast one organic polymer capable of binding to a metal surface throughoxygen and/or nitrogen atoms and selected from the group consisting ofmaleic anhydride/methyl vinyl ether copolymer and acrylic acid andmethacrylate monomer terminated by phosphate groups; wherein thetreatment solution is chromium-free and the organic polymer carries 0.1to 20% by weight, based on the total weight of the organic polymer, ofcovalently bonded groups which appear colored to the human eye.